a. Field of the Invention
The present invention relates in general to circuitry for vortex shedding flow meters and, in particular, to a new and useful circuit and method of driving the sensor connected to a vortex shedding flow meter to reduce energy consumption and heating of the sensor.
b. Description of the Prior Art
Vortex shedding flow meters are utilized to measure the volumetric flow of fluids by presenting a non-streamlined obstruction termed a bluff body in the flow path. As the flowing fluid separates around the obstruction, vortices are produced in the wake of the obstruction which alternate from one side of the obstruction to the other. The number of these vortices per unit time is directly proportional to the volumetric flow rate. The number of vortices thus can be counted to provide a measure of the flow rate.
It is known to utilize a continuously operating bridge circuit to sense the passing of these vortices. The bridge circuit usually has one resistor or other element which has a varying parameter such as resistance with the passage of each vortex. Circuit elements are connected to the bridge to count the thus sensed passage of vortices and to provide a signal which is proportional to the flow rate of the fluid to be measured.
Transformers are utilized to drive one side of the bridge and also to tap the signal from the other side of the bridge. When large driving voltages are utilized, the sensor bridge has a tendency to heat and lose accuracy due to drift and also impairs useful life. Moreover, many transmitter applications do not have this high power available on a continuous basis.
Thus an accurate vortex shedding frequency sensor was required which was drift free, over extended operating times.